Synthesis of Vinylic Sulfones in Aqueous Media

TMSCl-Promoted Sulfonylation of Propargylic Alcohols with Sodium Sulfinates for the Construction of (E)-1,3-Disulfonylpropenes and (E)-1-Sulfonylpropenols

A direct and novel transformation of propargylic alcohols with sodium sulfinates for the regio- and stereoselective synthesis of (E)-1,3-disulfonylpropenes and (E)-1-sulfonylpropenols was successfully developed in the presence of TMSCl under mild conditions. The preliminary mechanistic experiments demonstrated that the reaction underwent an unprecedented dual nucleophilic substitution/radical addition process, in which sodium sulfinates were used not only as nucleophiles but also as a sulfonyl radical source.

Synthesis of fused-pyran derivatives via a base-mediated annulation of bis-allenoates followed by auto-oxidation in air

We introduce, for the first time, an inorganic base-mediated cyclization and auto-oxidation of bisallenones/bisalkynones. This reaction is realized under mild conditions through precise control of the base and atmosphere, providing a wide range of structurally diverse fused-pyran derivatives with moderate to excellent yields. Utilizing KOH as the initiator under a nitrogen atmosphere, a series of novel cyclohexane-fused pyran derivatives was obtained as the primary product. In contrast, under aerobic conditions with Na2S as the catalyst, oxidative cyclization predominantly occurred, yielding cyclohexanone-fused pyran derivatives. The protocol also exhibits significant regioselectivity, particularly when asymmetric bisallenones/bisalkynones are selected as substrates.

Dehydrogenation Coupling and [3 + 2] Cycloaddition of Indolizines with Allenes in the Presence of Piezoelectric Materials under Ball Milling Conditions

A wide range of indolizines with allenes proceeded smoothly under mechanochemical-induced conditions via [3 + 2] annulation process, affording various substituted pyrrolo[2,1,5-cd]indolizines with good yield. The reaction efficiency was greatly improved by using a piezoelectric material as the charge transfer catalyst. The photophysical properties of the resulting pyrrolo[2,1,5-cd]indolizine was characterized.

Development and Applications of Water-Compatible Reactions: A Journey to Be Continued

ConspectusThe pursuit of novel and eco-friendly methods in organic synthesis is gaining prominence, with a strong emphasis on green transformations using renewable and sustainable resources. Among these environmentally conscious approaches, water-compatible reactions stand out for their many advantages. Water, as a solvent, offers unmatched abundance, cost-efficiency, and environmental compatibility compared to organic solvents. Its use eliminates the need for complex protection and deprotection steps for reactive functional groups in multistep synthesis and enables the use of water-soluble substrates like proteins and carbohydrates. Water-compatible reactions also provide opportunities to combine with enzymes, resulting in chemoenzymatic transformations that can increase efficiency. Additionally, these reactions facilitate site-specific modification and the bioconjugation of biomolecules, leading to bioconjugate therapeutics.Over nearly three decades, our research group has been dedicated to developing innovative water-compatible methodologies and concepts. This Account provides a comprehensive overview of our contributions since 1994. Our central strategy revolves around integrating green chemistry principles into our methods, focusing on (i) developing reactions that can operate under mild conditions, including room temperature, atmospheric pressure, and physiological pH; (ii) designing atom-economical reactions that minimize waste production; (iii) replacing toxic and flammable organic solvents with eco-friendly alternatives like water and ethanol; and (iv) reducing reliance on metals or halogenated compounds in specific reactions.In this Account, we detail our achievements in developing efficient methodologies in aqueous media, highlighting their scope, limitations, asymmetric control, and applications for synthesizing complex molecules and functionalizing peptides and proteins. Mechanistic investigations underlying these developments are also discussed when applicable. Furthermore, we offer insights into the reasoning behind our work and address future opportunities and challenges in this area of research. We hope that this Account will inspire continued interest and foster new breakthroughs. By exploring innovative and broadly applicable strategies that expand the water-compatible synthetic toolbox, we aim to pave the way for the truly green and sustainable synthesis of complex molecules and pharmaceuticals.

Copper(I)-Catalyzed Cross-Coupling of Arylsulfonyl Radicals with Diazo Compounds: Assembly of Arylsulfones

A novel copper-catalyzed cross-coupling of arylsulfonyl radicals with diazo compounds is described for the synthesis of various arylsulfones under mild conditions. In this reaction, the cheap, environmentally friendly, and readily available inorganic K₂S₂O₅ is employed as the sulfur dioxide source for providing arylsulfonyl radicals. In addition, a radical mechanism involving the insertion of sulfur dioxide with aryl radicals followed by the coupling of arylsulfonyl radicals with copper carbenes is proposed.

The Sulfinylsulfonation of alkynes for β-Sulfinyl alkenylsulfone

Here we report the first example of sulfinylsulfonation of alkynes to afford β-sulfinyl alkenylsulfone products with a broad substrate scope, excellent functional group compatibility, and high yield. Moreover, sulfinylsulfonation reaction of enyne can also be realized for constructing functionalized carbo- and heterocycles through a radical cascade cyclization process.

Visible-Light-Induced Tandem Reaction of Allenes with Selenesulfonates Leading to (E)-2,3-Disulfonylpropene Derivatives

A visible-light-induced tandem reaction of allenes with selenesulfonates was developed, providing (E)-2,3-disulfonylpropene derivatives in moderate to good yields. This reaction was featured with simple operation, good regioselectivity and stereoselectivity, and wide functional group tolerance. Photoinduced radical additions via energy transfer were proposed.

One-Pot Synthesis of N-Hydroxypyrroles via Soft α-Vinyl Enolization of (E)-β-Chlorovinyl Ketones: A Traceless Arylsulfinate Mediator Strategy

A traceless arylsulfinate mediator strategy has been developed to switch the reaction course of β-chlorovinyl ketones with N-hydroxyamine. The soft α-vinyl enolization of (E)-β-chlorovinyl ketones was conducted in the presence of sodium arylsulfinate to give transient alkenyl sulfones that in turn reacted with NH₂OH to give novel access to N-hydroxypyrroles. The mechanistic studies revealed the initial formation of oxazine intermediates that rearranged to thermodynamically stable aromatic products, N-hydroxypyrroles, under microwave-assisted heating conditions.

Synthesis of chiral sulfinate esters by asymmetric condensation

Achiral sulfur functional groups, such as sulfonamide, sulfone, thiol and thioether, are common in drugs and natural products. By contrast, chiral sulfur functional groups are often neglected as pharmacophores1-3, although sulfoximine, with its unique physicochemical and pharmacokinetic properties4,5, has been recently incorporated into several clinical candidates. Thus, other sulfur stereogenic centres, such as sulfinate ester, sulfinamide, sulfonimidate ester and sulfonimidamide, have started to attract attention. The diversity and complexity of these sulfur stereogenic centres have the potential to expand the chemical space for drug discovery6-10. However, the installation of these structures enantioselectively into drug molecules is highly challenging. Here we report straightforward access to enantioenriched sulfinate esters via asymmetric condensation of prochiral sulfinates and alcohols using pentanidium as an organocatalyst. We successfully coupled a wide range of sulfinates and bioactive alcohols stereoselectively. The initial sulfinates can be prepared from existing sulfone and sulfonamide drugs, and the resulting sulfinate esters are versatile for transformations to diverse chiral sulfur pharmacophores. Through late-stage diversification11,12 of celecoxib and other drug derivatives, we demonstrate the viability of this unified approach towards sulfur stereogenic centres.

Pyridine vs DABCO vs TBAB in Annulations of δ-Acetoxy Allenoates with Thioamides Leading to Dihydrothiophene, Thiopyran, and Thiazole Scaffolds

The same δ-acetoxy allenoates and thioamides, under DABCO, pyridine, or tetra-n-butyl ammonium bromide (TBAB) catalysis, undergo distinctly different annulations giving chemoselective routes to dihydrothiophene, thiopyran, or thiazole motifs. Thus, using pyridine in [3 + 2] annulation, dihydrothiophenes are obtained as essentially single diastereomers. By contrast, under DABCO catalysis, allenoates deliver thiopyran motifs in good to high yields through 6-exo-dig cyclization. In the thiazole forming [3 + 2] annulation, tetra-n-butyl ammonium bromide (TBAB) facilitates addition-elimination and 5-exo-trig cyclization in which β- and γ-carbons of allenoates participate to deliver thiazole cores exclusively with a Z-isomeric exocyclic double bond. A possible rationale for these observations is delved into.

Temperature Controlled Di- and Monosulfonylation of Propargyl Alcohols with Sodium Sulfinates: Switchable Access to (E)-Allyl, Vinyldisulfones and Propargyl Sulfones

A switchable di- and monosulfonylation of propargyl alcohols with sodium sulfinates is developed, which successfully affords (E)-allyl, vinyldisulfones and propargyl sulfones in good to excellent yields, respectively. The salient features...

Rongalite as C1 Synthon and Sulfone Source: A Practical Sulfonylmethylation Based on the Separate-Embedding Strategy

Rongalite has been used in several challenging synthetic transformations with operationally simple and effective protocols. However, the employment of multiple characteristics of rongalite in synthetic chemistry is comparatively little known. Herein we report a separate-embedding type sulfonylmethylation of sulfoxonium ylides in which rongalite concurrently acted as a sulfone source, C1 synthon, radical initiator, and potential reducing reagent for the first time. Notably, this facile and easy-handling reaction does not require a catalyst or prefunctionalized sulfonylmethylation reagents.

Catalytic Electrophilic Thiocarbocyclization of Allenes

An efficient approach via catalytic electrophilic thiocarbocyclization of allenes to construct indene-based sulfides with excellent regioselectivities is disclosed. The reactions were carried out at low temperatures by selenide catalysis in the presence of TMSOTf. Not only electrophilic arylthio reagents but also electrophilic alkylthio reagents worked well under these conditions. Furthermore, the method could be applied to intermolecular azidothiolation of allenes.

Easy Access to Allylic Sulfones Through Transition-Metal-Free Hydrosulfonylation Of Allenes

A Brønsted acid-mediated addition of (hetero)aryl and (cyclo)alkyl sodium sulfinates to N-allenyl derivatives, which proceeds in water, is described under very smooth conditions. This reaction provided a practical and efficient protocol for the regio- and stereoselective synthesis of allylic sulfones in an atom- and step-economic fashion.

Divergent Reactivity of δ- and β'-Acetoxy Allenoates with 2-Sulfonamidoindoles via Phosphine Catalysis: Entry to Dihydro-α-carboline, α-Carboline, and Spiro-cyclopentene Motifs

The reactivity of 2-sulfonamidoindoles with acetoxy allenoates under phosphine catalysis depends on the disposition of the acetoxy (OAc) group on the allenoate. In the temperature-controlled [3 + 3] annulations, δ-acetoxy allenoates afforded dihydrocarboline and carboline scaffolds with carbon-nitrogen nucleophilic 2-sulfonamidoindoles, in which allenoate serves as a β-, γ-, and δ-carbon donor. At room temperature (25 °C), dihydro-α-carboline motifs were obtained exclusively through Michael addition, 1,4-proton shift, isomerization, 1,2-proton transfer, phosphine elimination, and aza-Michael addition. The higher temperature (80 °C) cascade protocol using Ph₃P-Cs₂CO₃ combination involves addition-elimination, aza-Claisen rearrangement, tosyl migration, and aromatization as key steps to give α-carbolines containing tosyl functionality at the γ-carbon. In contrast, with β'-acetoxy allenoate, 2-sulfonamidoindole acts only as a carbo-nucleophile in (p-tolyl)₃P-directed [4 + 1] spiro-annulation, leading to five-membered spiro-carbocyclic motifs essentially as single diastereomers (dr >20:1) via chemoselective carbo-annulation.

Unconventional approaches for the introduction of sulfur-based functional groups

Organosulfur compounds have a pivotal role in the functionalities of many natural products, pharmaceuticals and organic materials. For these reasons, the search for new methodologies for the formation of carbon-sulfur bonds has been the object of intensive work for organic chemists. However, the proposed strategies suffer from various drawbacks, such as volatility, toxicity, and instability of the sulfur sources or the use of VOC solvents. In this review, we summarise the recent protocols which have the goal of obtaining sulfones, thioethers, thiazines, thiazepines and sulfonamides in an unconventional and/or sustainable way. The use of starting materials less invasive and toxic with respect to the traditional reagents, alternative solvents such as water, ionic liquids or deep eutectic solvents, the exploitation of ultrasound and electrochemistry, increasing the efficiency of the process, are reported. Moreover, representative reaction mechanisms are also discussed.